Identification of SRGt 062340.2-265751 as a bright, strongly variable, novalike cataclysmic variable

¹ Leibniz-Institut für Astrophysik Potsdam (AIP), An der Sternwarte 16, 14482 Potsdam, Germany
e-mail: aschwope@aip.de
² South African Astronomical Observatory, PO Box 9, Observatory, 7935, Cape Town, South Africa
³ Department of Astronomy, University of Cape Town, Private Bag X3, Rondebosch 7701, South Africa
⁴ International Centre for Radio Astronomy Research, Curtin University, GPO Box U1987, Perth, WA 6845, Australia
⁵ Dr. Karl Remeis-Sternwarte & Erlangen Centre for Astroparticle Physics, Friedrich-Alexander-Universität Erlangen-Nürnberg, Sternwartstr. 7, 96049 Bamberg, Germany
⁶ Space Research Institute (IKI) of Russian Academy of Sciences, Profsoyuznaya ul 84/32, 117997 Moscow, Russian Federation
⁷ Max-Planck-Institut für extraterrestrische Physik, Gießenbachstraße, 85748 Garching, Germany
⁸ Department of Physics and Astronomy, Texas Tech University, USA

Received: 22 April 2021
Accepted: 4 June 2021

Abstract

We report the identification and follow-up of the transient SRGt 062340.2–265751 detected with both instruments on board the Spektrum-Roentgen-Gamma mission. Optical spectroscopy of the G = 12.5 counterpart firmly classifies the object as a novalike cataclysmic variable (CV) at a distance of 495 pc. A highly significant TESS period of 3.941 h, tentatively identified with the orbital period of the binary, could not be found when the object was reobserved with TESS two years later. The newer high-cadence TESS data revealed quasi-periodic oscillations around 25 min, while ground-based photometry indicated periodic variability at 32 min. Located in very sparsely populated regions of color-magnitude diagrams involving X-ray and optical magnitudes and colors, the new object could be an X-ray underluminous magnetic CV, an intermediate polar, or an overluminous nonmagnetic CV. The lack of uniquely identified spin and orbital periods prevents a final classification. The site of X-ray production in the system, L_X,_bol = 4.8 × 10³² erg s^-1, remains to be understood given its high variability on long and short timescales.